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Thread: another 'my amp fuses keep blowing'

  1. #11
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    thanks for all the help everyone.

  2. #12
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    yayyy new amp works
    i have now earthed to the seat mounting points
    subs are going in 2morrow

    quick question
    whenever i turn off the ignition i get a sort of pop/crackle through the speakers

    what would be the cause of this?
    i imagine it will only be worse when the subs go in

    is it dangerous?
    is it a sign of somethings going to go wrong?
    is there a way around this?

  3. #13
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    Quote Originally Posted by soundman98 View Post
    the easiest way to figure out the jl components would be to use a ohm meter, but i believe that the 4 ohm statement should be correct for both the tweeter, mid, and crossover.
    remember that an Ohm Meter will be a DC measurement if resistance. A Speaker has an Impedance measurement which is an Ac measurement of many factors such as resistance, capacitance and inductance being a few. resistance just being one of them. and that resistance will change with frequency. it is not a set measurement. it will generally get higher (more ohms) at the the Fs of the driver(s) and the box tuning frequency. it will generally get lower around the crossover points.


    Anyway, you can use a Ohm meter to get a close idea of a woofer. an 8 ohm woofer typically measures around 5-6 ohms, a 4 ohm woofer maybe around 2-3 ohms etc.

    but measurements through a crossover with an ohm meter don't work as the crossover blocks DC from passing. Looking at the resistance of a system with say a woofer, midrange and tweeter with a 3 way crossover. the woofer see's a very complex load. but. in simple terms, the amp will "see" the impedance of each driver withing each drivers frequency range plus whatever loading the crossover adds.

    So lets really mess this up and take a look at what would happen. say you have a 2 ohm woofer, and 8 ohm midrange and a 4ohm tweeter. with crossover points of 300hz and 3khz and lets forget for the moment the mess this makes.

    the amp, will see only the 2ohm woofer woofer from 0 to 300hz, then the 4ohm midrange from 300hz to 3khz and then the 4ohm tweeter from 3khz to however high the tweeter will go.

    now this isn't 100% true as the drivers overlap a bit at the crossover frequencies. how much overlap depends on how many db per octave your crossovers are. and we haven't taken into account whatt he inductance and capacitance of the crossover does. but....you get the idea.

    Most better home speakers will have a chart with an impedance curve that looks pretty much like a roller coaster. peaks at the box tuning points and valleys around the crossover areas where the amp will see both drivers.

    To me it sounds like you had some speaker wires shorted to ground or, you had amp channels shorted together.



    Part of your comment i am confused about:
    2 6 inch JL audio splits (on the box says 4 ohms so i assume this includes both the tweeter and the woofer) in front doors
    2 alpine 2 way type S (4ohms) also in front doors. (these are connected in parallel to the JL crossover. so thats channel 1 from amp into jl crossover then from there to the alpines. the outputs on the xovers go to the appropriate woofer and tweeter)


    so you have one channel of the amp powering a set of JL audio speakers and the alpine speakers? that would then be a 2 ohm load.

  4. #14
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    Quote Originally Posted by mroverkill View Post
    remember that an Ohm Meter will be a DC measurement if resistance. A Speaker has an Impedance measurement which is an Ac measurement of many factors such as resistance, capacitance and inductance being a few. resistance just being one of them. and that resistance will change with frequency. it is not a set measurement. it will generally get higher (more ohms) at the the Fs of the driver(s) and the box tuning frequency. it will generally get lower around the crossover points.


    Anyway, you can use a Ohm meter to get a close idea of a woofer. an 8 ohm woofer typically measures around 5-6 ohms, a 4 ohm woofer maybe around 2-3 ohms etc.

    but measurements through a crossover with an ohm meter don't work as the crossover blocks DC from passing. Looking at the resistance of a system with say a woofer, midrange and tweeter with a 3 way crossover. the woofer see's a very complex load. but. in simple terms, the amp will "see" the impedance of each driver withing each drivers frequency range plus whatever loading the crossover adds.

    So lets really mess this up and take a look at what would happen. say you have a 2 ohm woofer, and 8 ohm midrange and a 4ohm tweeter. with crossover points of 300hz and 3khz and lets forget for the moment the mess this makes.

    the amp, will see only the 2ohm woofer woofer from 0 to 300hz, then the 4ohm midrange from 300hz to 3khz and then the 4ohm tweeter from 3khz to however high the tweeter will go.

    now this isn't 100% true as the drivers overlap a bit at the crossover frequencies. how much overlap depends on how many db per octave your crossovers are. and we haven't taken into account whatt he inductance and capacitance of the crossover does. but....you get the idea.

    Most better home speakers will have a chart with an impedance curve that looks pretty much like a roller coaster. peaks at the box tuning points and valleys around the crossover areas where the amp will see both drivers.

    To me it sounds like you had some speaker wires shorted to ground or, you had amp channels shorted together.



    Part of your comment i am confused about:
    2 6 inch JL audio splits (on the box says 4 ohms so i assume this includes both the tweeter and the woofer) in front doors
    2 alpine 2 way type S (4ohms) also in front doors. (these are connected in parallel to the JL crossover. so thats channel 1 from amp into jl crossover then from there to the alpines. the outputs on the xovers go to the appropriate woofer and tweeter)


    so you have one channel of the amp powering a set of JL audio speakers and the alpine speakers? that would then be a 2 ohm load.
    that is correct. the amps stable to 2 ohms
    seems thats all fixed as i had the speakers working today (although i haven't gone louder then 26)

    any info on the latest question
    with the popping/crackling noise i get when i turn off the car?
    btw: thanks for the info about the crossovers

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